Conventionally, there has been a method for controlling removal of secret data by encrypting and storing a file when a secret file is stored in the secondary storage apparatus of a user terminal. In this method, even if a file is removed, it does not mean that the information itself is removed because the file is encrypted. For example, Patent Document 1 (JP Patent Publication (Kokai) No. 11-149414 A (1999)) discloses an automatic file cryptograph system which interrupts to a file I/O processing of OS to automatically execute processing of encrypting and decrypting, and thereby makes the system convenient for a user.
In addition, there is a method which allows editing of a secret file and prevents information leakage by implementing an access control for, for example, a removable device and a printing device.
However, there is a trend that losing a mobile PC having a secret file of customer information and the like, which has been encrypted and stored in the mobile PC, will not be socially accepted even with the fact that the secret information is not at risk of leakage because it is encrypted. If a company has lost an encrypted file, the company must announce such a fact that the file has been lost, and is criticized seriously and socially. Then it is feared that even a life of the company might be lost. Thus, there is such a great need that secret information may be utilized and viewed, but not stored for a PC which can be lost, such as a mobile PC. However, the automatic file cryptograph system disclosed in the Patent Document 1 can not meet this need.
The present invention has been developed in consideration of such a circumstance, and provides a system which enables a more secure reference to information.